This invention relates to circular knitting machines, and in particular to needle selection in such machines, for example to produce embroidered, patterned or net stockings.
The invention provides a device and method for needle selection in which the selection is made at each yarn feed by rapidly and accurately separating those needles to be raised in order to seize the new yarn for working purposes, from those needles to remain inactivated at the lowest level.
In the known art the selection devices are fixed and operate on the vertical jacks which raise the needles into activation when said vertical jacks, during their rotation together with the cylinder, appear in front of the fixed selection station which precedes the fixed yarn feed station.
As a circular knitting machine has between 200 and 400 needles, between one and four or more yarn feed stations and a rotational speed of up to 1500 r.p.m., and may well require the selection to be made needle by needle, the selection device is vary complicated and difficult to construct, and also difficult to control.
The time available for setting, initiating and completing the selection is very small, being of the order of a few thousandths of a second, and determined by the small angular sector within which the rotating vertical jacks face the selection member, which for its part must be immediately ready to select those needles or more precisely those needle jacks which at that moment are presented to them.
Most recently, the solution to the problem has turned towards mobile selection devices rotating together with the circular machine, so that the time available for selection is not limited to the moment in which the jacks appear before the stationary selection device. In this manner each vertical jack is constantly presented to its selection member, so that the selection can take place in any angular position or at any time as required. In this manner the selection setting time is not so drastically small and the selection can be effected reliably and safely.
In Italian patent application 9314A/89, this needle selection is effected by controlling the radial position of the vertical jacks by means of corresponding horizontal jacks which slide radially in grooves provided in a circular ring structure surrounding the cylinder. The horizontal jacks are selected by electromagnetic retention devices, which are either energized or not energized. Those electromagnetic devices which are energized retain the horizontal jack in its most outer position to activate the corresponding needles, in that their vertical jack is left in its outer position to be lifted by the provided for this purpose. Those electromagnetic devices which are not energized do not retain the horizontal jack, and allow it to return inwards under the action of a thrust spring. Said jack in its turn urges the corresponding vertical jack inwards to leave its needle in the inactivation position. Thus one vertical jack, one horizontal jack and one selection electromagnet are provided for each needle of the circular machine.
In a circular machine the number of needles varies from about 200 to 400, as stated, and the whole assembly of needles, jacks and electromagnetic selection devices rotates together with the machine cylinder at a speed which can reach 1500 r.p.m.
Electrical power has to be fed to this rapidly rotating assembly, normally by sliding contacts, as do the selection commands for the needles, which have to lie in a precise attitude needle by needle before encountering the yarn feed stations, which are positioned at regular intervals about the cylinder.